Landing means for aircraft



Oct. 11, 1938. K.-BAUMANN Er AL 2,132,599

I LANDING MEANS FOR AIRCRAFT Filed Jan. 3l, 1936 W noemf @Eff/vee Fae mer/mL #www W nemvsmrrfe Patented Oct. 11, 1938 ,d Urrea LANDING MEANS Foa AiRcRArT' Karl Baumann, BaseLand Armin Ettinger, Birs-` felden, near Basel, Switzerland i `Application January 31, 1936, Serial No. 671,712.0-` j In Switzerland December 23, 1935 claims. iol. 2501-11) yThis invention relates to a Inetliod"` of and means forassisting the landing of airplanes. Y To assist the landing of aircraft when there is little or no visibility it is necessary for the pilot 5 `tor be 'notified in some form that he is in the proper direction for landing and that he is gliding .down along a path suitable for the particular `landing ground concerned, and for this purpose va method has already been proposed which makes lO'use of different levels in the radiation eld of a `transmitting aerial' or aerial combination, a transmitter beingprovided on the ground and a receiver in the airplane see for instance: E. Kramar;` The present state in the art of blind landloing of `airplanes using ultra-short waves in Europa. Proc. I. R. E., vol. 23, page' 1171, October 1935.

The primary disadvantages associated with this arrangement consist in the rst place in the fact 20 that the more sensitive of the two apparatus, viz.,` the receiver, is located `on the airplane, so that there are considerable interferenceslin the reception, `due chiefly to the ignition system ofA the engine.` To overcome these interferences the 25 transmission output must accordingly be-very high. Secondly, there is no possibility of controlling the glide of` theaircraft during the landing operation on the ground. f A

To avoid the disadvantages aforesaid it'has,

30 therefore, also been proposed to locate the transmitter on the aircraft and to provide the receiveA ing system on the ground, the landing glide of the aircraft being determined by a level of the receiving aerial system. 'IAhe receiving apparatus 35 controls automatically a .transmitter non the ground, and the controlA signals received by the aircraft, for example by means of a normal receiver, are made noticeableto the pilot either acoustically or optically.

40 `Nowinthis latter method, in whichthe exact horizontal and vertical line of movement of the aircraft when approaching the ground is deter" mined by the signals received, i. e., in which the gliding path is defined as level in the field of the 45 receiving aerial arrangement provided on the ground, it has been found that the glide becomes very ilat towards the end. In consequence there is always a certain danger'in association with 50 comparatively high points or obstacles situated in the line of ight in the immediate vicinity of the aerodrome. Y p l It is the object of the invention, therefore, to provide a method and means by which the line 55 followed by the airplane when gliding to' earth s may be adapted as `desired to local landing conditions.

`"The invention accordingly consists in the fact thatithe output potential of the receiver on the ground for thev horizontal navigation varies auto- 5 matically, from a certain point of approach of the landing airplane, theV amplication of the receiver in respect of theverticalnavigation, in such fashion that the pilot, in order to maintain constant the intensity of the signals received, is compelled to descend at an angle which intersects the levels infthe eld lof the receiving aerial in respect of the vertical navigation.` Y

The invention will* now be described more fully with reference to theaocompanying drawing, in which` Y Fig. l indicates diagrammatically Vthe landing operation in'accordance with the invention,

Fig. 2 is a circuit diagram relating to the transmission of the signals.

Fig. 3" is a diagrammaticv plan view` of the directional aerial for the receiver for horizontal navigation. A

Figl 4 is a diagrammatic view of the receiver for horizontal navigation and the change-over device interposed between it and the directional aerial.

Fig. 5 is a diagrammatic view hereinafter referred to. i

. For determining the horizontal direction of ap- 3o proach towards the landing ground there are employed the directional characteristics of two crossed` receiving loops R1 and R2. Fig. 3 shows these two' loops Rl'and R2 with their horizontal directional characteristics in plan. The circles in dotted lines represent the receiving characteristie of the loop R1 and the circles in full lines the receiving characteristic of the loop R2. The output potentials of the two loops, with equal construction of the loops, are alike when a wave arrives .in the direction PO which is the direction ofrlanding.V If now an airplane approaching the landing eld in ,the direction PO, which line of direction divides the angle between the planes of the two loops into two equal angles, transmits by means of atransmitter a continuous tone, then the output potentials created inthe two loops are alike. AIf there is a deviation from the proper landing direction towards the right,` the output potential of the one loop, owing to the transmission of a continuous tone by the ultra-short wave transmitter on the airplane, is greater than that of the other loop. Upon deviation towards the left the position is exactly vice versa. For the purpose of obtaininga greater relative sensitivity ing after rectification of the low-frequency output Y of the said receiver is employedV to control the amplitude of `a tone produced by a tone generator, the frequency of which differs from,r the modulating frequency of the ultra-short wave transmitter on the airplane.-`v Y This locally generated frequency, which is dependent as regards amplitude on the output of.r

the said receiver,is then applied as modulation tothe aerodrome transmitter,L Thesignalsof thev aerodrome transmitter may be received by the aircraft with a normal long-wave receiver. If the direction of the airplane exactly coincides with the landing direction, the two loops'r will be actedv upon equally by the ultra-short wave transmitter on the airplane.

Upon the changingover of the loops there` is then no jump in the sound intensity at the output of the receiver U. The modulation of the aerodrome transmitter corresponds, therefore, with acontinuous tone without jumpin intensity, and indicates to the pilot, who receivesthe signals with the long wave4 apparatus, that he is iiying inthe correct direction of approach. If his course deviates from the mid-position towards the right, the one loop isacted upon bythe ultrashortwavetransmitter'to a greater extent than theA other, and the one signal, forexam'ple the shorter one, will be louder thanthe other. Upon deviationV towardsthe left the longer signal will be `louder than the shorter one. In this way itis possible to distinguish between the two sides. For the` vertical navigation; another receiving fv aerialv arrangement on the ground isA acted upon by the waves transmitted bythe ultra-short wave transmitter on the airplane. An example for such anarrangement ofantennassee for instance Diamond and Dunmore: A radio beacon .and receiving system for vblind landing of aircraft. Proc.

I. R. E.,l vol. 19, Fig. 7, page 596, April 1931. There'is described an arrangementfor the transmittingcase', but allv concerning the vertical characteristic holds also` for the receiving case.

l The glide pathislaid down as anequalintensity linein the vertical characteristic of the receiving antenna arrangement. The direct current of the low-.frequently Output of this receiver on the ground controlsthe amplitude of` a second sound generator, the frequency of which differs from that of the sound generator previously. referred to. The output of, this second so und generator likewise modulates the aerodrome transmitter.

For thev purposeY of explanation it is assumed kthat an airplane is flying at a certain altitude :ln`

the direction ofk landing. The output potential of the ground receiver continuously increases, and.

in accordance with the method above described is notifledback to the airplane.

If the movementon thepart'of aninstrument in theairplane actuated bythe answer-back sigfashion that the instrument actuated by the answer-back continues to show the same extent of movement, in which case he glides down to the ground along the prescribed landing curve.

The two modulation tones (for horizontal and vertical navigation) are separated by low-frequency filter chains in the receiver on board the airplane.

It is also possible to provide .at a suitable point a receiver combined with an aerial arrangement,

which has such a vertical characteristic, -that Vwhen passed over bythe ultra-short wave trans- `mitter transmitting on board the aircraft develops for a brief interval an output voltage key- Aing a'thirdV tone generator and applying this` lowfrequency voltage as modulation frequency to the aerodrome transmitter. This modulation frequency, when received in the airplane provides indication that landing should be commencedv(marker signal).

Fig. 5 illustrates diagrammatically the methodv described in the foregoing. Hi represents the ultra-short wave transmitter in the aircraft, I the normal long Wave operating receiver with automatic sound-volume control in the aircraft, K are Ythe low frequency filter chains by means of which the answer-back signals ofthe aerodrome transmitter modulated with different sounds are separated,L and M are the indicating means for the horizontal and1vertical navigation, N represents the receiverfor the vertical navigation, R the low frequency output rectifier for the verticalr navigation, Trthe loop system for the horizontal navigation, S the changeover device for the loops, U the receiver for the horizontal-'navigation, and Weis ,theaerodrome operating trans- Referring now to` Fig. 1, the curvesV lY to 5 indicate different levels in the field of the receiving aerial V. The dilerent curves correspond with different valuesof the intensity of the field. 'I'he top curve indicates the greatest and the bottom curve the lowest intensity of the field.

In landing without the regulation provided for by the invention the line of flight would coincide with'one of the curves l to 5. If Vnow the amplification of the receiver on the ground for the Verticalv navigation is increased from .a certain point of approach, such as A, which corresponds with the distance Xfrom the aerial system for the vertical navigation, the pilot, in order that the outputof the ground receiver for the vertical navigation, and accordingly the intensity of Y Y This` method maybest be Vexplained in con- H junction with a particular formv of embodiment: Y

The ultra-short wave transmitter on the airplane acts on the ground receiversfo-r the marker signal,V the horizontal navigation and the vertical navigation. The aerial system of the receiver for the horizontalnavigation should be such that its output potential depends primarily on the distance of the airplane transmitter. The 'aerodrome receiver for the vertical navigation operates without regulation up to the moment when the airplane with the ultra-short wave transmittervv on boardtransmittingv flies over the anpoint of its characteristic.

tenna arrangement of ftheinarker signal receiver and so actuatesthefmarker signalywhichat the same time indicates by its location the nearest obstacle in 4the" direction of4 landing in thevicinityofthe aerodrome. Up to this point, therefore,

the airplaneindescending follows a normal level of the aerial systeinin vrespect of the vertical navigation.

When the airplane .with the ultra-short wave transmitter transmitting on 4board passes over the antenna system@ connected with the receiver" for themarker signal the antenna yields an input voltage to the `marker signal receiver. The output .voltage of `this' receiver is only present when the transmitteron boardvpenetrates thev vertical lobe of the vertical diagram of the associated antenna arrangement `of the marker signal receiver. This` output.. voltage switches on automatically by means of arelay the regulation :of amplification ofthe ground: receiver in respect of 'the `vertical navigation.4 The' voltage .regulat-` ing the amplification of the receiver for the vertical navigation is deducted from the output of thereceiver for the horizontal navigation. 'Ihis is; regulation voltage is substantially'proportional to Vthe distance of the airplane from the receiver for horizontal navigation. lIn the receiver for theV verticaliiavigation` are provided one or `more tubes having-a variable and adjustable amplification factor. The regulation voltage deducted from the output of the receiver for horizontal navigation is appliedto. the regulation grids of these. tubes thus alecting. the amplification of theV receiver for vertical navigation in proportion ofthe distance of the ultra-short wave transmitterv on board the airplane: to the' antenna system of the receiver for horizontal navigation;`

In Fig. 2, I is the receiver, whichcan be of the normal superheterodyne type, with its antenna system having a vertical characteristic with the main lobe directed upwards.` l 2 is the receiver for the horizontal navigation with its. two crossed loops.` 3 is a variable high-frequency` pentode provided for instance as .a stage in the intermedii ate frequency amplifier of the receiver for the vertical navigation or as` an input stage of this receiver.

ceiver, in the second case to the frequency of the With the aid of resistance 5 the working point of the tube 3 is set at a point of low amplication factor, the resistance 5 giving a fixed bias to the regulation grid of this tube, when the upper two contacts of relay 6 are closed. So long as the marker signal receiver has no input voltage applied thereto due from the transmitter on board the airplane the tube works constantly at this When iiying over the antenna system of the marker signal receiver, however, the relay 6, actuated by the output voltage of the marker signal receiver, by closing the two lower contacts and opening the two upper ones, applies a part of the output voltage of the horizontal navigation voltage, which is tapped at the potentiometer 8, to the regulation grid of the tube 3 of the vertical navigation receiver. The potentiometer is so adjusted, that, when the `marker signal receiver is flown over at the correct altitude, the potential tapped by way of the In the first case the grid circuit lisA tuned tothe intermediate frequency of the rethe amplication of the receiver for the vertical navigation becomes all the greater the nearer the aircraft approaches the receiver` for horizontal navigation, thus giving a glide path steeper than without regulation. It is clear, that `the relay 6 must be of such a construction, that the contacts are fixed in their position, when once the two upper are opened and the two lower ones are closed, because the current through the coil of relay 6 flows only during the time, when the airplane with theultra-short wave transmitter transmitting on board isftransversing the vertical lobe of the diagram of the marker signal antenna system. Such relays are known (Impulse relays). When the landing is made the contacts must be brought back to their initial position. This can be eiected by giving an impulse over the coil of thelrelay given Aby the wireless operator of the aerodrome'. 'A

If theantenna system of the marker signal receiver is not passed at exactly Vthe correct altitude, then the voltage tapped at `potentiometer I does not exactly compensate the voltage tapped at potentiometer 8. Thus a jump occurs in the amplification of the tube 3 upon the switching over of the relay 6. From the answer-back message received by' the-.pilot `the latteris able to ascertain whether the machine was flying over the marker signal receiver too high or too low. A certain allowance may nevertheless be made in this connection whilst still permitting of a safe landing. This allowance may be marked on the vertical navigation instrument inthe airplane. The pilot then merely `requires to navigate the machine vertically in such fashion upon landing that the diierent movement of the instrument remains constant. i i i The angle of the glide pathmay be adjusted by means of the potentiometer 1 applying a more or less greater part of the-output voltage of the receiver for'horizontal navigation as regulation voltage to the receiver for vertical navigation, thus making the angle of the glide path to follow more or less steep. By means of resistance 5 it isV possible to vary the length of the regulated path. If for instance the resistance 5 is set at a-value `such that only a small voltage increase puts the amplification of the tube 3 to its highest possible value, then the last part ofthe glide path is not regulated, because a further increase of the regulation voltage does not increase further the .amplication of tube 3. Since the horizontal navigation is performed according to the method in which in a certain direction the signals supplement each other to form a steady line, care must be taken in the output of the horizontal navigation receiver that in the case of small deviations from the exact horizontal path the regulating potential corresponds with the mean value of the two signals, which may be accomplished by a netwo-rkwith corresponding time constant.

What we claim as new and desire to secure by Letters Patent is:

1. In means for assisting the landing of aircraft, means for transmitting signals from the aircraft, directionally sensitive aerials on the ground by which said signals are received, means for establishing answer-back signals from ground to aircraft, a vertical navigation receiver on the ground and connected with one of said aerials, and means including a horizontal navigation receiver connected to another of said aerials for so varying automatically from a predetermined point of approach of the aircraft the amplication of said vertical navigation receiver to vary sitive aerial thereforlocated on the ground; aY

horizontal navigation receiver anda directionally sensitive aerial therefor, said receivers; being constructed to receive signals transmitted from' theV aircraft, an, aerodrome transmitter and. an,

E aerial'thereforfor transmitting answer-backl signals to the aircraft; operative means connecting saidvvertical navigationY receiver and said horizontal navigation receiver respectively tosaid aerodrome transmitter for affecting a characteristic'jofthe ans Wer-back transmission, a receiver ontheaircraft forreceiving the answer-back signais, meansfor varying theY amplicationof said' vertical navigation receiver in accordance with.

the output-.of thehorizontal navigation receiver,-r

and instruments on the aircraft forindicating the horizontal and vertical navigation necessaryin view-of the signals received; o

3; In Ia means forassisting the lancling'oi:` aircraft, a transmitter'on board the aircraft, di-

eli),

rectionallysensitive aerialsfon theground,l a ver-- ticalnavigation receiver, a horizontal/navigationV receiver andamarker signal receiver; each'freceiver beingconnectedto ay diieren-t one of saidfv aerials, the said receivers `being adapted to re .ceive signals transmitted by. theaircraft, an

answer-back signal transmitter, operating connections between said marker signal receiver and said' horizontal and said vertical navigation receivers,V operating connections between saidfhorizontal and vertical' navigation receivers respectiveiyand rsaid answer-back transmitter for affecting a characteristic oftransmissionl ofu ansWer-back signals to theV aircraftV automatically, a receiver on the-aircraft-for receiving the saidanswer-back signals, a relay operatively connectedfwith said marker signal receiver'for energization bythe output voltage thereof', said; relay includingfmeans,for-coupling the vertical navigation receiver with the output circuit of the horizontal navigation receiver so `that the output potential thereof` Will act on the amplification Yof the vertical navigation receiver, andjinstruments,`

onwtheeaircraft indicating the horizontal andvertical navgationlnecessary inaccordancezwith the signals,,receivedi Y f Y 4.. Inav means o forgaaissisting;.theI landing o of aircraft; aftransmitter on boardftheaircraft; directionallyfsensitive ,aerials 'onthe' ground; a vertical ,navigation receiver-connected with, one of saidv aerials, a horizontal navigation receiver and a; marker signal` receiver connectedA with others;` of said-aerials, themarker signal receiver`V being actuatedby signals-transmitted bythe aircraftwhen; the aircraft. ilies, overf-thesame, an; ansWer-back--` signal transmitting means, 'meansl operatively connectingsaidi receivers =with one another and with saidianswer-back signal: transmitting means for transmitting answer-back signals :to-the aircraft automatically, ag receiver; onI thev aircraft; for receiving said; answer-back; signals, a relay. operatively connectedwith said'marker signal ret-- ceiver for, energization. by, the output voltage thereof; said: relay,including ,means for coupling the vertical navigation receiver` with the outputy circuit; of the-,horizontal navigation receiver, and means for adjusting the effective actionof, said, horizontal navigation. receiverf.-

craft,, a, transmitter;l on board; the' aircraft, di-

rectionallyv sensitive aerials on the ground,Y a

verticalV navigation l receiver connected' With one of said .aerials and having an intensity regulating tube, a` horizontal. navigation receiver and a marker.I signal receiver-connectedwith others of said aerials, said marker signal receiver being actuated in response to. signalstransmitted by the .aircraft when the latter flies over said marker signal receiver, ran answer-back` 'signal transmitter, operatingconnectionsbetween said mark; er signal receiver.' and. saidhorizontal; andV said vertical navigation receivers respectively and, said answer-back signal transmitter` and including-means to couplevthe intensity regulating tube with. the output circuit of thehorizontal navigation receiver, a variableresistance acting inthe circuit ofthe tube ofthe vertical navigation receiver for varying the working. point of the'characteristic 'of'saidt tube, andiinstruments onthe. aircraft indicating the horizontal and vertical navigation necessary, in, accordancev withV the signals received.

v KARL BAUMANN.

ARMIN.: ETTINGER.

Y 25. 5'. Ina means forassistingthelandingof air- 

